Yes it is the flat bottem, yes it is both teeth rattling and potentially dangerous, boats have been abandonded not because they a sinking but because the motion was so sevear people where breaking limbs (see reports from the Fasnet). it doesnt need a F8 just a short steep chop, F4 and a couple of knots of tide the wrong way will make life horrenduse and breack crockery. On the other hand they are very fast and exciting, they are big dingies and sail like them.
One thing to watch is the plated load, if you are used to traditional heavyweights you are use to being able to chuck anything on board without worrying. When I looked at the load level on a Bavaria 34 I found it was less all up than the wt of my ground takle and that had to include fuel, stores and all the boat kit. You need to be strick about keeping it light and if you go over stability can be seriously jepodised. (From memory I think the bavaria had a max load about 1/2 ton above light ship wt)